1. Field of the Invention
The present invention relates to audio replay systems and particularly to audio replay systems in live environments.
2. Description of the Related Art
In typical rock concerts, there are high dynamics to the effect that e.g. the singer moves a lot on stage. The same often applies to the guitarist. On the other hand, in such a performance environment, the loudspeakers are disposed statically. Thus, it cannot be avoided that the singer with his microphone as well as, for example, the guitarist with the microphone attached to his guitar is sometimes closer to loudspeakers and sometimes further away from loudspeakers. While the case where the microphone is far away from a loudspeaker is unproblematic, the case where a microphone is very close to a loudspeaker is very problematic. Since there is a high amplification in the signal path from microphone to loudspeaker, launching the loudspeaker signal into the microphone leads to the microphone/loudspeaker system starting to oscillate. Such an oscillation is expressed as feedback at a certain frequency. It always occurs when the amplitude and phase condition is fulfilled. The specific phase condition, which is currently best fulfilled, determines the frequency, which is typically relatively high, so that a feedback is audible as loud howling. This howling is not only awkward for the listeners but also for the artists.
Expressed in a signal theoretical way, there is a channel from one or several loudspeakers to one or several microphones, which is strongly variable in time.
Known feedback suppressing techniques mix audible feedback sounds into the microphone and use filters to suppress a starting feedback.
Alternative feedback suppressing techniques use a so-called pitch shifting technique to shift the feedback to inaudible parts of the spectrum, so that stable feedback sounds are avoided.
While the first solution requires a short feedback to trigger a suppression, the other solution effects in some case a strange sound, which, for example, makes singing and intonating for artists difficult.
Particularly in multichannel systems, the two mentioned feedback suppressing solutions are very problematic, if not even impracticable.